The invention relates to an insert for a clearance volume between a cylinder liner and a cylinder head, and to an internal combustion engine containing the insert.
Inserts and internal combustion engines of the type discussed here are known. An internal combustion engine of this kind comprises at least one cylinder, which comprises a cylinder liner, and furthermore comprises a cylinder head, which closes off the cylinder on a side situated opposite a piston arranged movably in the cylinder liner—as seen in the axial direction of the cylinder liner—and has a second end face facing first end face of the cylinder liner. The cylinder liner is held in the internal combustion engine by being pressed against a “balcony seat” of a crankcase by the cylinder head in the region of a liner collar. Here, the contact forces are transmitted via a liner collar region arranged radially on the outside in order to avoid shearing off a radially inner region of the cylinder liner. In order to absorb the contact forces, a force introduction element is provided in the radially outer region of the cylinder liner, said element typically being designed as a copper-plated iron ring. It is preferably via this element that all the force flows from the cylinder head to the liner collar of the cylinder liner. To avoid contact forces also acting in the radially inner region of the liner collar, a clearance is preferably provided between the first end face and the second end face, thus overall producing an annular gap which—as seen in the radial direction—is open toward an interior of the cylinder liner. This gap, which is also referred to as a clearance volume, has a negative effect on combustion in a combustion chamber of the cylinder because unburnt residual gas collects or an undefined mixture consisting of air, combustion gas and products of incomplete combustion can form in the clearance volume. In particular, it is possible that a pressure wave caused by combustion in the combustion chamber will ignite residual gas in the clearance volume, leading to combustion knock. Moreover, it is possible for lubricant, especially oil, to collect in the clearance volume, leading to soot formation and the accumulation of glow points, which, in turn, enter the combustion chamber in an undefined way and can lead there to uncontrolled ignitions or to knock. The proportion of unburnt hydrocarbons is increased by quenching in the gap, leading to increased hydrocarbon emissions in the exhaust gas of gas engines with homogeneous mixture compression. It is therefore desirable to minimize the clearance volume where possible.
For this purpose, European Patent Application EP 1 918 559 A2 discloses an insert, which is designed either as part of a cylinder head gasket or separately from a cylinder head gasket. In order to ensure that force flows only in a radially outer region of the cylinder liner, the region of the insert filling or sealing off the clearance volume is of weakened design and/or formed from a softer material in comparison with a region in which contact forces are introduced. Particularly owing to manufacturing tolerances in series production, however, it is not possible in this way in all cases actually to seal off the clearance volume without a gap and at the same time to ensure that contact pressure forces are introduced only in the radially outer region provided for this purpose. Even the material which is softer or weakened in comparison with the material provided in the region for the introduction of force still has a hardness which makes it necessary to provide at least a slight gap for tolerance matching if all effects on the path of the forces is to be avoided. Although the clearance volume is reduced in this way, it is not closed in an effective manner.